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Hypothermia can be induced in humans and some animals for the purpose of protecting various organs and tissues (e.g., hear, brain, kidneys) against the effects of ischemic, anoxic or toxic insult. For example, animal studies and/or clinical trials suggest that mild hypothermia can have neuroprotective and/or cardioprotective effects in animals or humans who suffer from ischemic cardiac events (e.g., myocardial infract, acute coronary syndromes, etc.), postanoxic coma after cardiopulmonary resuscitation, traumatic brain injury, stroke, subarachnoid hemorrhage, fever and neurological injury. Also, studies have shown that whole body hypothermia can ameliorate the toxic effects of radiographic contrast media on the kidneys (e.g., radiocontrast nephropathy) of patients with pre-existing renal impairment who undergo angiography procedures.
One method for inducing hypothermia is by endovascular temperature management (ETM) wherein a heat exchange catheter is inserted into a blood vessel and a thermal exchange fluid is circulated through a heat exchanger positioned on the portion of the catheter that is inserted in the blood vessel. As the thermal exchange fluid circulates through the catheter's heat exchanger, it exchanges heat with blood flowing past the heat exchange in the blood vessel. Such technique can be used to cool the subject's flowing blood thereby resulting in a lowering of the subject's core body temperature to some desired target temperature. ETM is also capable of warming the body and/or of controlling body temperature to maintain a monitored body temperature at some selected temperature. If a controlled rate of re-warming or re-cooling from the selected target temperature is desired, that too can be accomplished by carefully controlling the amount of heat added or removed from the body and thereby controlling the temperature change of the patient.
In most if not all commercially available heat exchange catheters, the heat exchange fluid flows through an inflow lumen of the catheter shaft, then enters one end of the catheter's heat exchanger, then flows through the heat exchanger, then exits from the heat exchanger into an outflow lumen located within the catheter shaft. In general, greater heat exchange efficiency is accomplished when the heat exchange fluid flows through the catheter's heat exchanger in a direction that is opposite the direction in which the blood is flowing through the blood vessel in which the heat exchanger is positioned. Thus, the type of catheter used and/or the selection of which port(s) of the catheter should be used for inflow and outflow, respectively, is sometimes dictated by the intended sites of entry and positioning of the catheter. For example, in some cases, a heat exchange catheter is inserted into a femoral vein and advanced to a position where its heat exchanger is within the subject's vena cava. In such cases, the blood flowing normally through the vena cava will progress from the proximal end of the heat exchanger toward the distal end of the heat exchanger. Thus, in those cases, it will generally be desirable for the heat exchange fluid to enter the catheter's heat exchanger at its distal end and flow back toward the proximal end of the heat exchanger (i.e., counter to the direction of blood flow). If, however, the heat exchanger catheter were inserted into a femoral artery and advanced to a position where its heat exchanger is within the descending aorta, blood flowing normally through the descending aorta would progress from the distal end of the heat exchanger toward the proximal end of the heat exchanger. Thus, in those cases, it would generally be desirable for the heat exchange fluid to enter the catheter's heat exchanger at its proximal end and flow distally toward the distal end of the heat exchanger (i.e., again counter to the direction of blood flow).
Also, in heat exchange catheters where the heat exchange fluid flows in only a single direction through the catheter's heat exchanger, the heat exchange fluid typically is shunted to one or the other end of the heat exchanger through an internal lumen of the catheter. While traveling though that internal lumen the heat exchange fluid is exchanging only minimal if any heat with the flowing blood.
The following U.S. patents, the entire disclosures of which are expressly incorporated herein by reference, disclose various intravascular catheters/systems/methods useable for altering or maintaining a subject's body temperature: U.S. Pat. Nos. 6,881,551 and 6,585,692 (tri-lobe catheter), U.S. Pat. Nos. 6,551,349 and 6,554,797 (metal catheter with bellows), U.S. Pat. Nos. 6,749,625 and 6,796,995 (catheters with non-straight, non-helical heat exchange elements), U.S. Pat. Nos. 6,126,684, 6,299,599, 6,368,304, and 6,338,727 (catheters with multiple heat exchange balloons), U.S. Pat. Nos. 6,146,411, 6,019,783, 6,581,403, 7,287,398, and 5,837,003 (heat exchange systems for catheter), U.S. Pat. No. 7,857,781 (various heat exchange catheters).
There remains a need in the art for the development of new heat exchanger catheters and methods which offer improved heat exchange efficiency and/or ease of use.